Work around issue with ember-cli calling Testem.hookIntoTestFramework

This is normally handled for folks by ember-qunit, but
@ember/test-helpers has to handle it for itself.

We need to get this fixed over in ember-cli...

ember-cli-build.js

@@ -9,7 +9,7 @@ module.exports = function (defaults) {
       testGenerator: 'qunit',
     },
     trees: {
-      vendor: null,
+      vendor: 'tests/dummy/vendor',
     },
   };
 

tests/dummy/vendor/ember-cli/test-support-suffix.js

@@ -0,0 +1,15 @@
+/** globals runningTests */
+/*
+  used to determine if the application should be booted immediately when `app-name.js` is evaluated
+  when `runningTests` the `app-name.js` file will **not** import the applications `app/app.js` and
+  call `Application.create(...)` on it. Additionally, applications can opt-out of this behavior by
+  setting `autoRun` to `false` in their `ember-cli-build.js`
+*/
+runningTests = true;
+
+/*
+  This file overrides a file built into ember-cli's build pipeline and prevents
+  this built-in `Testem.hookIntoTestFramework` invocation:
+
+  https://github.com/ember-cli/ember-cli/blob/v3.20.0/lib/broccoli/test-support-suffix.js#L3-L5
+*/

tests/test-helper.js

@@ -1,3 +1,4 @@
+/* globals Testem */
 import QUnit from 'qunit';
 import { registerDeprecationHandler } from '@ember/debug';
 import AbstractTestLoader from 'ember-cli-test-loader/test-support/index';
@@ -125,3 +126,7 @@ QUnit.assert.deprecationsInclude = function (expected) {
 };
 
 QUnit.start();
+
+if (typeof Testem !== 'undefined') {
+  Testem.hookIntoTestFramework();
+}